Glossary
Email validation
Checking whether an address can actually receive mail.
Validation is layered. Syntax: is it shaped like an address? Domain: does the domain exist and publish MX records (mail servers)? Mailbox: does this specific inbox exist — checkable only by talking SMTP to the server, which is slower and sometimes blocked.
Between syntax and mailbox live the practical checks that catch most damage: disposable domains, role accounts, typo domains, and accept-all domains.
In ListFunnel
ListFunnel runs syntax, disposable, role, typo, and live MX checks free on every plan, and marks each address valid, risky, or invalid with the reason spelled out.